1. Field of the Invention
Applicant's invention relates to apparatuses for retrieving liquid samples from reservoirs of liquid.
2. Background Information
Groundwater pollution is an ever-growing concern in today's environments, and the need for groundwater monitoring is increasing, especially around chemical storage facilities, land fills, military bases, airports, and underground storage tanks.
The typical groundwater monitoring program consists of a series of monitoring wells located at different points around the margin of an aquifer, in close and distant proximities from the potential contamination source. Each monitoring well consists of a well casing which lines the well bore, the hole extending from the ground surface to the groundwater.
At least until very recently, most monitoring samples have been taken through the use of devices known as bailers. A bailer is an elongated, slender tube which is sized to pass through the well casing of a test well. The insertion end of an advanced bailer includes a one-way valve which allows water to flow into the bailer as it is lowered into the well casing, but hinders effluent flow as the bailer is lifted from the water.
Bailers have been in widespread use in the groundwater sampling process because they are inexpensive to purchase, inexpensive to fabricate, portable, simple to operate, and require no external power source. However, inherent in the presently-known bailer designs, is the inability to control the flow rate of the sample—a serious problem in light of relatively new knowledge concerning factors affecting the quality of samples taken in test wells.
It has been determined that if the extraction rate exceeds the recharge rate, the sample may be compromised through various means, including the increase of the turbidity of the sample, the mixing of stagnant and fresh water in the well, and the disturbance and re-suspension of settled solids. The results of the sample analysis then may be skewed, showing either higher or lower levels of contamination in the groundwater then actually exist, depending on the characteristics of the contaminant. As a result, Federal and state governments now require that samples of ground water be extracted at a rate not exceeding the recharge rate of the sampling well. Resulting guidance documents now state that bailers are ill-suited for low flow. Thus, use of conventional bailers for test well sampling is very nearly obsolete.
The preferred method for test well sampling now involves the use of pumps. Ironically, although the pump flow rates are easily controlled, the problems associated with using pumps at test well sites are the very reasons that most samplers changed from using pumps to using bailers in the past. Pumps are expensive, harder to clean and operate, and require an external power source. Pumps also have go through general maintenance procedures to maintain the life of the pumps, increasing the cost.
In view of the foregoing, it would well serve those involved in test well monitoring to provide some means by which test well sample may be taken with the simplicity and economy of bailers, yet still comply with the new low-flow sampling requirements.